Place the coriander, mustard and celery seeds in a mound on one side of a kitchen towel. Fold the towel over the seeds. Pound with a heavy saucepan until the spices are crushed. Pour into a 2-quart glass measure. Add the vinegar, 2 1/4 cups water, the salt and tarragon. Cover tightly with microwave plastic wrap. Cook in a microwave at 100% for 7 minutes, or until boiling. Prick the plastic to release the steam.

Remove from the oven and uncover. Divide the radishes evenly among the jars, fitting the pieces snugly, upright, in them. Place half a shallot in the center of each jar. Pour enough vinegar mixture over the radishes to cover, leaving 1/2 inch headroom in each jar.

Arrange the filled jars around the edge of the carousel. Cook at 100% for 12 minutes, or until just tender. Remove from the oven and cover with the lids. Let cool slightly.

Refrigerate at least overnight, or up to several months. Serve chilled.